Nigerian Islamist group Boko Haram is showing early signs of weakening, reducing the risk of a spillover into neighboring countries in West Africa's Sahel band, the head of France's military operation in the region told Reuters on Sunday.

General Jean-Pierre Palasset said there are signs that the militant group's strength has peaked - even though it has staged a series of deadly raids in Nigeria since the country's military announced a ceasefire deal last week, as well as battling government forces in neighboring Cameroon.

Palasset said in an interview that Maiduguri, capital of Nigeria's Borno state, had been at risk of falling into the insurgents' hands last month but he felt the situation had stopped deteriorating since then.

"The pressure's coming off near Maiduguri," he said at the French military headquarters for the region in Chad's capital, N'Djamena. "Apart from a few border villages Boko Haram is very much contained in Borno."

The Nigerian military also raised hopes that more than 200 schoolgirls kidnapped in April would be released under the deal it said had been struck with Boko Haram. However, the girls have yet to be freed and the violence has intensified.

Suspected Boko Haram militants killed at least 17 people and abducted dozens in a series of attacks in the central region of Borno State, the head of a local administration said on Sunday.

Cameroon's defense ministry spokesman said separately in a statement on Sunday that its troops had killed 39 Boko Haram fighters during three different incidents on Friday in the far north region near the border with Nigeria.

Boko Haram has fought a bloody five-year revolt mostly in northeastern Nigeria to carve out an Islamist enclave in the religiously-mixed nation. It has also carried out attacks in Niger as well as northern Cameroon.

Fears that it could destabilize the region have prompted the leaders of Chad, Nigeria, Benin, Niger and Cameroon to set up a multinational force to tackle the insurgents.

Palasset heads France's Operation Barkhane, a separate drive which is focused on fighting Islamic militants in the Sahel, a sparsely populated arid strip running the breadth of West Africa. But the 3,000-strong force also carries out surveillance work on Boko Haram whose stronghold is less than 100 km (60 miles) away from its base.

Any decision to begin direct military action against Boko Haram would have to come from Paris, Palasset said. Patricia Adam, head of the defense commission to the French National Assembly, said it was not France's job to lead operations against the group.

"It's the role of African armed forces. They have just asked for help with logistics and intelligence and general know-how from our forces to help them with their own operations," she said on Sunday during a visit to the base.

Palasset, who has served in Afghanistan and Ivory Coast, said that the security situation in northern Mali was degenerating, partly due to the fact that such groups were finding sanctuary in southern Libya.

France deployed its troops to Mali in 2012 after Islamic extremists seized the desert north. Troops have since been redeployed, although France still assists a U.N. peacekeeping force there.